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Aperture Array LNA Cooling

(How best not to cool an LNA!). Aperture Array LNA Cooling. Is it economically viable (or even physically possible) to cool the tens of thousands of front-end LNAs used in an SKA aperture array station?. Presentation Overview: 1 – Aperture Array Review 2-PAD 2 – LNA Cooling Costing Model

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Aperture Array LNA Cooling

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  1. (How best not to cool an LNA!) Aperture Array LNA Cooling Is it economically viable (or even physically possible) to cool the tens of thousands of front-end LNAs used in an SKA aperture array station? Presentation Overview: • 1 – Aperture Array Review • 2-PAD • 2 – LNA Cooling Costing Model • physics and features • results • 3 – LNA Cooling Measurement • description • results Presentation Overview

  2. 1000 SKA Reference Design 100 SKADS Benchmark 10 Field of View (deg2) 1 0.1 0.01 0.001 0.1 1 10 100 Frequency (GHz) SKADS Benchmark Scenario • Overall SKA concept • Low Frequency(0.1-0.3GHz)Sparse Apertura Array • Mid Frequency(0.3-1.0GHz)Dense Aperture Array • High Frequency(1.0-20GHz)Small Dishes • Aperture arrays are the only technology that provide survey speeds great enough to allow deep HI surveys • FoV = 250deg2 • Benchmark document available to download online at: • http://www.skads-eu.org/p/memos.php 1 – Aperture Array Review

  3. Aperture Array Concept 1 – Aperture Array Review

  4. Aperture Array Concept Look out for talk by:Georgina Harris 1 – Aperture Array Review

  5. Aperture Array Electronics Front-end PCB • Look out for talks by: • Chris Shenton (digital), Tim Ikin (analogue) 1 – Aperture Array Review

  6. Aperture Array Sensitivity • SKADS benchmark scenario document: • predicts the cost of an SKA aperture array station to be 3484k€ • assumes a Tsys of 50K for mid-frequency aperture array • a saving of 200k€ can be made if Tsys is reduced to 40K (§8.4) • Reducing Tsys • “Vital to get below 50K” Peter Wilkinson • Tsys might even be greater than 50K • future developments will see noise LNA decrease (14K from previous talk) • however cooling may still be required especially at high frequencies • cooling will also deliver temperature stabilisation 1 – Aperture Array Review

  7. front-end PCB coax to antenna twisted pair to receiver cooling block cooling lines plastic casing plastic casing o-ring track cooling block hose fittings milled fluid channel Aperture Array LNA Cooling • Possible concept for cooling the front-end module using a metallic cooling block front-end PCB warmfluid out coldfluid in 1 – Aperture Array Review

  8. Cooling Costing Model • The costing model / simulation code: • includes physics dealing with thermodynamics and hydrodynamics • costing includes: non-recurring expenses, replacement, electrical power • does not include: labour costs, no uncertainty analysis • written as a simple Matlab script (should be easy to convert, eg. Python) • might be able to become a ‘design block’ in the general SKA costing model • Assumptions / principle limitations • best estimates for input parameters used, some more inaccurate than others • chiller cost is assumed to be linearly proportional with power consumption, more costing ‘data points’ required to make a more accurate relationship • chiller cooling capacity efficiencies assumed to be equal for small and large chillers, more ‘real’ chiller specifications data are required • The Matlab script is currently available to download online at: • http://www.physics.ox.ac.uk/users/schediwy/cooling/ 2 – Cooling Costing Model

  9. Cooling Costing Model • For the results in this presentation the code is configured to: • compare cost of a cooling system with the total cost SKA aperture array as specified in the SKADS Benchmark Scenario document (3500k€/station) • compare the power consumption with total station use (1000kW/station) • Three scenarios are compared: • 1 chiller located at the centre of the aperture array – “Model A” • 16 chillers distributed throughout the aperture array – “Model B” • 256 chiller distributed throughout the aperture array – “Model C” • The Matlab script is currently available to download online at: • http://www.physics.ox.ac.uk/users/schediwy/cooling/ 2 – Cooling Costing Model

  10. Key: • chiller • pipe ‘D’ • pipe ‘C’ • pipe ‘B’ Cooling “Model A” • SKA aperture array station • Model A • chillers = 1 • pipe ‘D’ = 16 • pipe ‘C’ = 256 • pipe ‘B’ = 4096 • pipe ‘A’ = 65536 ~60m 2 – Cooling Costing Model

  11. Key: • chiller • pipe ‘D’ • pipe ‘C’ • pipe ‘B’ Cooling “Model B” • SKA aperture array station • Model B • chillers = 16 • pipe ‘D’ = 0 • pipe ‘C’ = 256 • pipe ‘B’ = 4096 • pipe ‘A’ = 65536 ~60m 2 – Cooling Costing Model

  12. Key: • chiller • pipe ‘D’ • pipe ‘C’ • pipe ‘B’ Cooling “Model C” • SKA aperture array station • Model C • chillers = 256 • pipe ‘D’ = 0 • pipe ‘C’ = 0 • pipe ‘B’ = 4096 • pipe ‘A’ = 65536 ~60m 2 – Cooling Costing Model

  13. LNA cooling block Individual Component Heat Power Absorption Total System Heat Power Absorption pipe A pipe A pipe C pipe D pipe B total cooling capacity available from the chiller pipe A pipe B pipe B pipe C pipe C pipe D pipe D LNA cooling block pipe A pipe B pipe C pipe D Features – Heat Absorption • Assumed ambient temperature 30°C, desirable LNA temperature −20°C • Cooling much below this temperature is not possible with a glycol/water mixture • The chiller cooling capacity was adjusted to compensate for the total heat power absorbed by the cooling system • Insulation thickness was increased until the LNA was the dominant factor 2 – Cooling Costing Model

  14. pipe C pipe D pipe B pipe A Total System Heat Power Absorption LNA cooling block pipe A pipe C pipe D pipe B total cooling capacity available from the chiller pipe A pipe B pipe C pipe D LNA cooling block pipe A pipe B pipe C pipe D Features – Heat Absorption • Assumed ambient temperature 30°C, desirable LNA temperature −20°C • Cooling much below this temperature is not possible with a glycol/water mixture • The chiller cooling capacity was adjusted to compensate for the total heat power absorbed by the cooling system • Insulation thickness was increased until the LNA was the dominant factor 2 – Cooling Costing Model

  15. pipe ‘C’ext = 100mmint = 20mm pipe ‘D’external radius = 150mminternal radius = 50mm pipe ‘B’ext = 58.5mmint = 6.5mm pipe A0.82m3 pipe ‘A’ext = 34mmint = 2mm pipe B2.17m3 pipe D5.02m3 pipe C2.57m3 Features – Fluid Pipes • Pipe and insulation dimension: • Fluid volumes: 2 – Cooling Costing Model

  16. pipe A pipe C pipe D pipe B LNA cooling block pipe A pipe D pipe D pipe C pipe B pipe D chiller pipe C pipe C LNA cooling block pipe B pipe B pipe A pipe A 0 1 2 3 4 5 6 7 8 9Position in Loop Features – Pressure/Flowrate • Chiller pressure must be great enough to drive fluid through cooling system • If there is too much pressure resistance the chiller flow rate will decrease • Flowrate was set so that Reynolds number is above 10,000 for all pipes • Dominated by inertial forces, viscous forces are minimised, turbulent flow 2 – Cooling Costing Model

  17. Model A60.0k€ (1.7%) • Model B 51.1k€ (1.5%) • Model C44.0k€ (1.3%) 6.6k€ 17.5k€ 6.6k€ 6.6k€ 9.9k€ 17.0k€ 16.1k€ 9.9k€ 9.9k€ 7.4k€ 2.7k€ 14.1k€ 1.6k€ 7.4k€ 4.0k€ 7.4k€ 7.4k€ 2.7k€ Cooling Model Cost Results • All cooling models only cost a small fraction of the total aperture array • Model C results in the lowest price, mainly due to the reduction in coolant used • limitation: model currently does not take into account the difference in cooling efficiency (coefficient of performance) of different classes of chillers 2 – Cooling Costing Model

  18. Electrical Power Consumption • Model A= 42.5kW × 1= 42.5kW • All models require only a small fraction (~4%) of the electrical power of the total aperture array (~1000kW) • Because of chiller assumption electrical power consumption of all models is very similar • Balance could change when chiller efficiencies are considered in detail • Model B= 2.57kW × 16= 41.1kW • Model C= 0.152kW × 256= 38.9W 2 – Cooling Costing Model

  19. Cooling the LNA PCB • Close-up photo of the Avago LNA showing the cold finger in contact with the PCB thermocouple probe GaA LNA cold finger in contact with the PCB 3 – Experimental Cooling Work

  20. Cooling the LNA PCB • The housing used to trap nitrogen to eliminate water condensation as the PCB warms-up to room temperature LNA PCB cold finger LN2 reservoir 50Ω terminator 3 – Experimental Cooling Work

  21. LNA Noise Temperature • Plot of the broad-band noise temperature of the LNA PCB recorded at three different LNA temperatures (−50°C, −10°C and +30°C) 3 – Experimental Cooling Work

  22. LNA Noise Temperature • Plot of LNA noise temperature of the LNA PCB at 700MHz measured at 17 different LNA temperatures 3 – Experimental Cooling Work

  23. Conclusions / Further Work • Conclusions • cooling 10,000’s of LNA is not physically ridiculous • cooling could be economically beneficial • cost a small fraction of the full aperture array (<2%) • electrical power use is a small fraction of the full aperture array (~4%) • Further Work • only three models were studied in detail; further optimisation of parameter space may result in • more work required on some cost inputs, particularly chiller assumptions • presently work on low-loss potting compounds to minimise condensation problems • The Matlab script is currently available to download online at: • http://www.physics.ox.ac.uk/users/schediwy/cooling/ Conclusions

  24. Questions? • The Matlab script is currently available to download online at: • http://www.physics.ox.ac.uk/users/schediwy/cooling/ Presentation End

  25. Extra Slides 4 – Extra Slides

  26. power supplies spectrum analyser 50Ω cold load copper coax gain chain v02 liquid nitrogen bath LNA Cooling Measurement • Photo of the experimental set-up used to measure the noise temperature of the LNA at various LNA temperatures 4 – Extra Slides

  27. Physics Used in Model • Prandtl number • coolant specific heat • coolant dynamic viscosity • coolant thermal conductivity • Reynolds number • coolant density • coolant dynamic viscosity • coolant flow velocity • pipe hydrodynamic diameter • Hagen-Poiseuille Law • coolant volumetric flow rate • coolant dynamic viscosity • pipe length • pipe cross-sectional area • Heat transfer coefficient • coolant thermal conductivity • pipe Nusselt number • pipe hydrodynamic diameter • Dittus-Boelter correlation • Reynolds number • Prandtl number • Heat power absorbed • heat transfer coefficient • ambient temperature • coolant initial temperature • insulation thickness • insulation thermal conduction • pipe surface area 4 – Extra Slides

  28. Current Limitations of Model • Insulation • Chiller flowrate large enough so that Reynolds number is above 10,000 for all pipes • means: flow is dominated by inertial forces, viscous forces are minimised, flow is turbulent • Cooling agents other than a glycol-water mixture would be too expensive, therefore minimum temperature limited to about −30°C • Incompressible fluid – very small effect • Laminar flow - • Wall friction – Darcy-Weisbach equation – easy to include in the future • Joint/Corner effects • Chiller efficiencies 4 – Extra Slides

  29. 3 Different Cooling Models • Schematic representation of three models investigated using a Matlab cooling and costing simulation pipe D pipe B pipe A pipe C x16 x16 x16 x16 antennapairs Model A1 central chiller chillers subtiles 1 16 256 4096 65536 large pipe small pipe x16 x16 x16 antennapairs Model B16 distributed chillers subtiles chillers 16 256 4096 65536 • The physical layout of three concepts are shown on the next slide large pipe small pipe x16 x16 antennapairs subtiles chillers Model C256 distributedchillers 256 4096 65536 4 – Extra Slides

  30. 3 4 Cascade Element: 1 2 50Ω Terminator Copper Coax Gain Chain v02 Spectrum Analyser Avago LNA Cascade Analysis • Factors affecting Tsys: • sky temperature • front-end LNA • rest of system 4 – Extra Slides

  31. SKADS Station Data Flow 4 – Extra Slides

  32. Nitrogen Atmosphere • A photo of the demo-board after warming back up to room temperature excess condensation collects on cold finger no condensation visible on PCB 4 – Extra Slides

  33. LNA Temperature Increase LN2 evaporated Cold Finger Removed 4 – Extra Slides

  34. Avago LNA – Testboard 1 4 – Extra Slides

  35. Aperture Array Mounting 2.56m 4 – Extra Slides

  36. ~13mm ~4mm ~13mm ~13mm CAT 7 and Cooling 30 Leads ~35mm Low DensityPoly Pipe 13mm X 100M: A$43.02  CAT 7 37 Leads 37Leads ~13mm 4 – Extra Slides

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